Electric switch



Dec. 21, 1965 3,225,160

P. BARKAN ELECTRIC SWITCH Filed Oct. 25, 1963 CURRENT 1' United States Patent Ofiice 3,225,169 Patented Dec. 21, 1965 3,225,160 ELECTRMZ WITCH Philip Barkan, Lima, Pa., assignor to General Electric Company, a corporation of New York Filed Oct. 25, 1963, Ser. No. 319,040 9 Claims. (Cl. 200-87) This invention relates to an electric switch and, more particularly, to means for inhibiting the tendency of the switch contacts to weld together under high current conditions.

In most switches, there is a wipe spring behind one of the contacts tending to hold the contacts in high pressure engagement while they are closed. When current flows through the closed contacts, magnetic forces varying directly with current magnitude are developed that typically tend to force the contacts apart against the opposition of the wipe spring. If the current is high enough, these magnetic forces will overcome the wipe spring and actually drive the contacts out of engagement. Such separation of the contacts is referred to hereinafter as contactpopping. When the contacts so separate or pop, the magnetic contact-separating forces are reduced, and the wipe spring responds to this reduction in force by driving the contacts back into engagement.

Reengagement of the contacts under these conditions is frequently accompanied by welding together of the contacts. This is the case because contact-separation produces an are between the contacts that melts their opposed surfaces, and subsequent reengagement of the contacts forces these molten surfaces into high pressure engagement, producing a weld upon solidification. This weld is highly objectionable because it tends to block a subsequent switch-opening operation.

The usual approach to preventing such contact-welding is to apply a sufficient hold-closed, force to the contacts to overcome the highest magnetic forces that are developed tending to force the contacts apart, thus preventing the contacts from popping. This approach is limited by the extremely high forces that are required to prevent contact-popping under high current conditions.

An object of the present invention is to provide an arrangement which can prevent such contact-welding without requiring the high forces needed to prevent contactpopping under high current conditions.

.In carrying out my invention in one form, I provide an electric switch comprising a pair of contacts that are relatively movable into and out of engagement with each other. Means including a switch operating mechanism is provided for producing engagement of the contacts when the switch operating mechanism is operated to a closed position. One of the contacts is adapted to pop out of engagement with the other of said contacts in response to magnetic contact-separating forces developed when the instantaneous current flowing through the contact exceeds a predetermined value. Spring means acting on said one contact permits it to move out of engagement with the other contact while the switch operating mechanism is in closed position but forces said one contact back into engagement with the other contact when said contact-separating forces diminish. Magnetic means responsive to current flow through said contacts delays reengagement of said one contact with the other contact by said spring means until the current through said contacts reaches substantially Zero. This delay in reengagement permits the opposed contact surfaces that have been melted by arcing to cool sufficiently to solidify, and this prevents substantial contact-welding upon reengagement.

For a better understanding of my invention, reference may be had to the following description taken in conjunction with the accompanying drawing, wherein:

FIG. 1 is a cross sectional view of a switch-fuse combination embodying one form of my invention.

FIG. 2 is a sectional view through the line 22 of FIG. 1.

FIG. 3 is an enlarged view of the contacts of the switch of FIG. 1.

FIG. 4 is a graphical representation of certain current relationships present in the apparatus of FIG. 1.

FIG. 5 is an enlarged view of a portion of a slightly modified switch.

FIG. 6 is a sectional view taken along the line 6-6 of FIG. 5.

FIG. 7 is a View similar to FIG. 6 but illustrating another modified form of the invention.

Referring now to FIG. 1, there is shown a switch-fuse combination 10 comprising a fuse 12 connected in series with a switch 14. This switch-fuse combination 10 is connected in a power circuit 16 having series related sections connected to opposite terminals 17 and 1.8 of the switch-fuse combination. The fuse 12 is intended to serve as an interrupting device for interrupting any excess currents that might flow through the power circuit 16. The switch 14, on the other hand, has no appreciable currentinterrupting ability and is used merely for disconnecting the fuse from the right hand section of the power circuit 16 and for reconnecting the fuse to this power circuit section as the need arises. In FIG. 1 the switch 14 is shown in its closed position.

Referring to FIG. 1, the switch 14 comprises a pair of cooperating contacts 29 and 21 shown engaging each other in their closed position. Contact 20 is a stationary contact suitably joined to a conductive strap 23, which, in turn, is fixed to an electrical insulator 24. The other contact 21 is a movable contact suitably joined to the outer end of a conductive switch member 25. The conductive switch member 25 supports the movable contact 21 and also carries currents between the movable contact and the other terminal 18 of the switch. A flexible conductor 26 of a conventional type electrically interconnects terminal 18 and the adjacent end of switch member 25. Terminal 18 is mounted on a suitable insulator 27.

The switch member 25 is pivotally mounted at 29 on an actuating member 30, which, in turn, is pivotally mounted on a stationary pivot 32 carried by the terminal 18. Switch-opening is effected by driving this actuating member 30 in a clockwise direction about its pivot 32, and switch-closing is effected by driving the actuating member in a counter-clockwise direction about its pivot 32 into the position shown in FIG. 1. A compression spring 34 is positioned between switch member 25 and the actuating member 30 to serve as a wipe spring for urging the movable contact 21 into engagement with the stationary contact 20 while the switch is closed. This wipe spring 34 permits a limited amount of overtravel of the actuating member 30 at the end of a closing stroke after the contacts 20 and 21 have engaged.

During switch-opening, opening forces are transmitted from the actuating member 30 to the switch member 25 through a bolt 34 that is fixed to the switch member 25 and extends freely through an opening in the actuating member 30. A stop 36 on this bolt 34 will be engaged by the back surface of the actuating member 30 to transmit opening force to the bolt 34 from the actuating member during a switch-opening operation.

Movement of the actuating member 30 between its open and closed positions is effected by a suitable switch operating mechanism shown at 40. This operating mechanism 40 comprises a pair of links 42 and 43 pivotally joined together by a pivot 44 at one end of each link. The opposite end of link 42 is pivotally connected at 45 to the actuating member 30, and the opposite end of the link 43 is pivotally mounted on a stationary pivot 46.

An actuating spring 48 of the tension type is connected between the pivot 44 and a movable operating pin 49. The operating pin 49 can be moved along a path determined by a guide slot 50 by suitable operating means (not shown). To open the switch, the operating pin 49 is moved from the bottom of guide slot 50 to the top. This shifts the line of action of spring 48 from the bottom side to the top side of stationary pivot 46, thus permitting the spring to drive the link 43 in a closing direction about the stationary pivot 46. This clockwise motion of link 43 pulls the link 42 to the right, driving the actuating member 30 and the switch member in a clockwise opening direction.

Closing of the switch is effected by returning the operating pin 49 from the top of guide slot 50 to its illustrated position. When the line of action of spring 48 is shifted downwardly past the stationary pivot 46, the spring returns the switch parts to the illustrated closed position. A suitable stop 52 engages the link 43 to limit its movement in a closing direction after it has effected contact-engagement.

When current flows through the closed contacts 21, 20, magnetic forces are developed that tend to force the contacts apart against the opposition of the wipe spring 34. These forces result primarily from the tendency of the current path through the contacts to constrict at the point of contact engagement, as shown in FIG. 3", where portions of the current path are designated by the arrows 60. Current flowing through these loop-shaped portions of the current path will develop forces of magnetic repulsion between the arms of the loop that tend to force the contacts apart. These magnetic forces vary in magnitude as a direct function of the current magnitude. If the current is high enough, these magnetic forces will overcome the wipe spring 34 and actually separate the contacts, i.e., will cause contact-popping. The switch-operating mechanism 40 remains in its closed position during such contact-popping, being held there by the actuating spring 48.

When the contacts separate or pop, the above-described current constricting effect is reduced, and the magnetic contact-separating forces are correspondingly reduced. In conventional switches, this reduction of force permits the wipe spring, such as 34, to drive the contacts immediately back into engagement.

Reengagement of the contacts under these conditions is frequently accompanied by Welding together of the contacts. This is the case because the above-described contact-separation produces a high current are between the contacts that melts the opposed surfaces, and reengagement of the contacts forces these molten surfaces into high pressure engagement. This produces a weld when these molten surfaces solidify upon cooling when current flow is terminated.

Current flow is terminated in the apparatus of FIG. 1 by fuse 12. This fuse is of a conventional construction that enables it to interrupt alternating current at an early current zero following initiation of the high current, preferably the first current zero. Since the con structional details of the fuse form no part of the present invention, these are not shown in the drawing. All that is shown is an insulating casing 60 having opposed terminals 62 and 63 at its opposite ends. These terminals 62 and 63 are interconnected by fusible elements (not shown) embedded in an arc-extinguishing material contained in the casing 60.

Refer now to the curve I of FIG. 4, which shows the alternating current flowing through the switch-fuse combination during a large overcurrent. T-he fuse will blow to initiate an are at a predetermined instantaneous value of current designated X, but current continues flowing through the switch-fuse combination via the are at least until the first current zero at Z. The current that fiows through the contacts 20, 21 during this interval causes the contact-popping or separation referred to hereinabove.

In conventional switches, the contacts will be forced back into engagement when the current reaches a value such as Y, and this will result in the above-described contactwelding.

But I prevent this contact-welding by delaying reengagement of the contacts until their molten surfaces have cooled sufficiently to solidify. This will prevent any substantial welding together of the contacts upon reengagement. For achieving this delay in contact-reengagement, I provide magnetic means 70 which is responsive to current flow through the contacts 20, 21 to hold the contacts out of engagement until the current falls to substantially Zero as shown at Z in FIG. 4.

This magnetic means 70 comprises a core 71 of a generally U-shaped form, as best seen in FIG. 2. This core 71 is made of a soft iron or some other low retentivity magnetizable material and is rigidly fixed to stationary structure 75 by suitable means (not shown). The core 71 comprises two spaced apart legs "72 and a bight portion 73 connecting these legs '72 together. An open-mouthed recess 74 is present between the legs '72.

The current flowing through switch member 25 will produce a magnetic field thereabout, as shown at 77 in FIG. 2. The upper portion of this magnetic field extends about the conductor 25 via the iron core 71, and this results in a region of higher flux density at the lower side of the switch member 25 than at the upper side. This will result in a magnetic force urging the switch member 25 upwardly into the recess 74. Another way of explaining this upward magnetic force is that the conductor 25 will move in a direction to decrease the reluctance of the magnetic circuit for the flux generated by current flowing through the conductor 25. Movement of the conductor 25 toward the bight portion 73 of the core decreases the reluctance of this magnetic circuit, and thus the magnetic force urges the conductor 25 toward the bight portion 73 of the core.

This magnetic force on the conductor 25 varies directly with the magnitude of the current through the con ductor 25, and is insufficient under normal current conditions to overcome the wipe spring 34. However, when an abnormally high current flows through the switch member 25, a relatively high magnetic force is developed. This force combined with the contact-popping force described in connection with FIG. 3, overcomes the wipe spring 34 and separates the contact 21 from its mating contact 20. As explained previously, this contactseparation produces an are between the contacts through which current continues to flow as shown at I in FIG. 4. The contact-popping force drops when the contacts separate, but the force developed by the magnetic means 70 continues to hold the contact 21 separated from the contact 20.

Assume now that contact-separation has occurred in response to a high current through the switch member 25 and contacts 20, 21. The movable contact 21 will be held in its separated position by the magnetic means 70 until the current I depicted in FIG. 4 has reached substantially the zero point Z. At this instant or slightly thereafter, the wipe spring 34 will drive the contact 21 back into engagement with the other contact 20. By this time, the contact surfaces that had been melted by the are drawn upon contact-separation will have cooled sufficiently to solidify, and their reengagement will produce no appreciable contact-welding. In the usual case, the fuse 12 will interrupt the current at the first current zero, and the interrupting process will therefore have been completed without contact-welding at the contacts 20 and 21.

If another half cycle of current should flow, the magnetic means 70 will perform in the same manner to prevent contact-welding. With respect to this additional loop of current, the polarity of the current does not affect the magnetic forces developed since these forces depend primarily upon flux density, and flux density is substantially independent of the polarity of the current. In this latter regard, the low retentivity of the magnetizable material of the core assures that the flux density will be substantially the same for a given value of current whether such value is negative or positive.

For a given value of current, the force developed at the magnetic means increases as the switch member 25 moves upwardly and continues to increase until the switch member 25 completely enters the recess 74. Since the switch member in its closed position of FIG. 2 is positioned slightly outside the recess 74, it will not then be subjected to as high a magnetic opening force as when it enters the recess. This relationship (i.e. normal positioning of the switch member 25 outside the recess 74 instead of within it) is advantageous in that it raises the current level at which contact-separation will occur. The fact that the highest forces for a given value of current are developed when the switch member 25 enters the recess is also advantageous in enabling the magnetic means 70 to continue holding contact 21 out of engagement with contact despite the drop in current that occurs as natural current zero is approached. It is not essential that the contact 21 be prevented from starting to move back into engagement with the other contact prior to current zero but only that it be prevented from actually engaging the other contact until substantially current zero. Since a finite amount of time will be required by the contact 21 to reach the other contact, reengaging movement can begin even slightly before current zero. In a preferred form of the invention, the combined mass of the movable switch member and contact 21 is sufiiciently high to delay reengagement of the contacts until at least a millisecond beyond the instant at which current zero is reached (assuming that no further current flows). In those cases where current flow continues past the first current zero, this relatively high mass of the movable contact parts 25, 21 prevents the contacts from reengaging at any current zero that is followed by an immediate resumption of current. Reengagement is delayed until immediately after the instant at which the final current zero is reached.

Referring to FIG. 1, it will be noted that the bight portion 73 of the magnetic core 71 does not extend across the full width of the core. This relationship leaves an opening in the bight portion through which the switch member 25 can travel during switch-opening and closing without interference from the magnetic means 7 9.

Although up to this point I have described the magnetic means 74 as controlling the movable contact 21, it is to be understood that it can instead be used to control the other contact 20. For example, assume that it is the contact 20, instead of the movable contact 21, that is backed up by the wipe spring 34 as shown in FIG. 5. Here, the contact-supporting member 23 is pivotally mounted at 23a for limited movement and the wipe spring 34 urges the contact 20 upwardly into engagement with the movable contact 21. A suitable stationary stop 3'7 limits the extent of such upward movement when the contacts are disengaged during opening. In this modification, as shown in FIG. 6 the core 71 is located with its legs defining an upwardly-opening recess into which the contact-supporting member 23 will be magnetically moved in response to high currents. After contacts 20 and 21 have separated, the continued fiow of current through the arc between the contacts and the member 23 will result in continued magnetic forces on the member 23 that hold the contact 20 out of engagement with contact 21. This magnetic force will hold the contact 20 out of engagement with contact 21 until sufficient cooling of the molten contact surfaces has occurred to prevent appreciable contact-welding upon reengagement. In this modification of FIGS. 5 and 6, it is assumed that the movable switch lever 25 has no wipe spring of its own and is rigidly connected to the operating mechanism in such a manner that it is held stationary While the operating mechanism is in its closed position of FIG. 1.

FIG. 7 illustrates an arrangement similar to that of FIGS. 5 and 6 except that additional magnetic means 7% is provided tending to oppose the magnetic means 7%. The magnetic field about the conductor 23 is divided substantially equally between the cores 70 and 70a so long as the contact supporting member 23 is in its normal position of FIG. 6. Thus, with member 23 in its normal position, there is little net magnetic force resulting from the core 70 and 70a tending to urge the contact-supporting member 23 downward, even with relatively high currents through the contact-supporting member 23. But should the contact-supporting member 23 be moved downwardly, as would result from contactpopping, a sharp increase in the net magnetic force acting in a downward direction will occur. This follows from the fact that the contact-supporting member 23 moves into the recess of the lower magnet and away from the recess of the upper magnet, thus increasing the pull of the lower magnet and decreasing the pull of the upper magnet. The advantage of the arrangement of FIG. 7 is that the magnetic means 70, 70a does not substantially lower the current level at which contact popping will occur since it exerts no substantial contact-separating force on the contacts until they separate for some other reason, such as popping. After such separation, the magnetic means of FIG. 7 holds the contacts 20 out of engagement with contact 21 until the molten surfaces of the contacts can cool sufficiently to prevent contactwelding upon reengagement.

While I have shown and described particular embodiments of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from my invention in its broader aspects, and I therefore, intend in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electric switch comprising:

(a) a pair of contacts that are relatively movable into and out of engagement with each other,

(b) means including a switch-operating mechanism coupled to a contact for producing engagement of said contacts when said switch-operating mechanism is operated to a closed position,

(c) one of said contacts popping out of engagement with the other of said contacts in response to magnetic contact-separating forces developed when the instantaneous current flowing through the contacts exceeds a predetermined value,

(c') means for holding said switch-operating mechanism in said closed position during high currents that cause said one contact to pop out of engagement with said other contact,

(d) spring means coupled to said one contact and urging it toward said other contact, said spring means permitting said one contact to move out of engagement with said other contact while said switchoperating mechanism is in closed position and for forcing said one contact back into engagement with other contact,

(e) and magnetic means responsive to current flow through said contacts for delaying reengagement of said one contact with the other contact by said spring means until the current through said contacts reaches substantially zero,

(f) said spring means urging said one contact in a direction toward said other contact irrespective of the distance that said one contact moves away from the other contact while said switch-operating mechanism is in its closed position, whereby said spring means consistently returns said one contact into a position of engagement with said other contact after the flow of high current that causes contact-popping.

2. The switch of claim 1 in which said one contact has a sufficiently high mass to delay reengagement of said '7 one contact with said other contact until at least a millisecond after the instant at which current zero is reached.

3. An electric switch comprising:

(a) a pair of contacts that are relatively movable into and out of engagement with each other,

(b) means including a switch-operating mechanism coupled to a contact for producing engagement of said contacts when said switch-operating mechanism is operated to a closed position,

(c) one of said contacts popping out of engagement with the other of said contacts in response to magnetic contact-separating forces developed when the instantaneous current flowing through the contacts exceeds a predetermined value,

(c) means for holding said switch operating mechanisin in said closed position during high currents that cause said one contact to pop out of engagement with said other contact,

(d) said disengagement producing an are between said contact that melts opposed surfaces of said contacts,

(e) spring means coupled to said one contact and urging it toward said other contact, said spring means permitting said one contact to move out of engagement with said other contact while said switchoperating mechanism is in closed position and for forcing said one contact back into engagement with said other contact,

(f) and magnetic means responsive to current flow through said contacts for delaying reengagement of said one contact with said other contact by said spring means until the contact surfaces melted by arcing have cooled sutficiently to prevent substantial contact-welding upon reengagement.

(g) said spring means urging said one contact in a direction toward said other contact irrespective of the distance that said one contact moves away from the other contact while said switch operating mechanism is in its closed position, whereby said spring means consistently returns said one contact into a position of engagement with said other contact after the flow of high current that causes contact-popping.

4. The switch of claim 3 in which a conductive switch member is fixed to said one contact for carrying current to and from said one contact, and said magnetic means comprises a generally U-shaped core of low retentivity magnetizable material having an open-mouthed recess into which said switch member is movable to decrease the reluctance of the magnetic circuit for the flux generated by current flowing through said switch member, motion of said one contact out of engagement with said other contact causing said switch member to move in a direction into said recess.

5. The switch of claim 4 in combination with second magnetic means for opposing the tendency of said first magnetic means to move said switch member into said recess, said second magnetic means having an effectiveness that decreases as said switch member moves into the recess of said first magnetic means.

6. The switch of claim 4 in which said switch member is coupled to said operating mechanism and is movable through a closing stroke in response to a closing operation of said operating mechanism.

7. The switch of claim 4 in which said other contact is a movable contact coupled to said operating mechanism so as to be moved thereby and said one contact is the generally stationary contact that remains fixed while said other contact is moved through an operating stroke,

8. The switch of claim 3 in which a conductive switch member is fixed to said one contact for carrying current to and from said one contact, and said magnetic means comprises a generally U-shaped core of low retentivity magnetizable material having an open-mouthed recess into which said switch member is movable to decrease the reluctance of the magnetic circuit for the flux generated by current flowing through said switch member, said U- shaped core being so positioned that said switch member is located slightly outside of said recess when said contacts are in engagement and said switch member moves toward said recess when said one contact moves out of engagement with said other contact.

9. In a switch-interrupting device combination that comprises an interrupting device for interrupting high electric currents and a switch in series with said interrupting device through which current flows while said interrupting evice is performing an interrupting operation,

(a) said switch comprising a pair of contacts that are relatively movable into and out of engagement with each other,

(b) means including a switch-operating mechanism coupled to a contact for producing engagement of said contacts when said switch-operating mechanism is operated to a closed position,

(c) one of said contacts popping out of engagement with the other of said contacts in response to magnetic contact-separating forces developed when the instantaneous current flowing through the contacts exceeds a predetermined value high enough to cause said interrupting device to operate,

(c') means for holding said switch-operating mechanism in said closed position during high currents that cause said one contact to pop out of engagement with said other contact,

(d) spring means coupled to said one contact and urging it toward said other contact, said spring means permitting said one contact to move out of engagement with said other contact while said switchoperating mechanism is in closed position and for forcing said one contact back into engagement with said other contact when said magnetic contactseparating forces diminish,

(e) and magnetic means responsive to current flow through said contacts for delaying reengagement of said one contact with the other contact by said spring means until the current through said contacts reaches substantially zero,

(f) said spring means urging said one contact in a direction toward said other contact irrespective of the distance that said one contact moves away from the other contact while said switch-operating mechanism is in its closed position, whereby said spring means consistently returns said one contact into a position of engagement with said other contact after the flow of high current that causes contact- P pp References Cited by the Examiner UNITED STATES PATENTS 1,764,369 6/1930 Van Sickle 200-87 2,182,864 12/1939 Frank 20087 2,679,561 5/1954 Thompson 200-87 3,065,317 11/1962 Streater 200-87 BERNARD A. GILHEANY, Primary Examiner.

JOSEPH J. BAKER, Assistant Examiner. 

1. AN ELECTRIC SWITCH COMPRISING: (A) A PAIR OF CONTACTS THAT ARE RELATIVELY MOVABLE INTO AND OUT OF ENGAGEMENT WITH EACH OTHER, (B) MEANS INCLUDING A SWITCH-OPERATING MECHANISM SAID CONTACTS WHEN SAID SWITCH-OPERATING MECHANISM IS OPERATED TO A CLOSED POSITION , (C) ONE OF SAID CONTACTS POPPING OUT OF ENGAGEMENT WITH THE OTHER OF SAID CONTACTS IN RESPONSE TO MAGNETIC CONTACT-SEPARATING FORCES DEVELOPED WHEN THE INSTANTANEOUS CURRENT FLOWING THROUGH THE CONTACTS EXCEEDS A PREDETERMINED VALUE, (C) MEANS FOR HOLDING SAID SWITCH-OPERATING MECHNIXM IN SAID CLOSED POSITION DURING HIGH CURRENTS THAT CAUSE SAID ONE CONTACT TO POP OUT OF ENGAGEMENT WITH SAID OTHER CONTACT, (D) SPRING MEANS COUPLED TO SAID ONE CONTACT AND URGING IT TOWARD SAID OTHER CONTACT, SAID SPRING MEANS PERMITTING SAID ONE CONTACT TO MOVE OUT OF ENGAGEMENT WITH SAID OTHER CONTACT WHILE SAID SWITCHOPERATING MECHANISM IS IN CLOSED POSITION AND FOR FORCING SAID ONE CONTACT BACK INTO ENGAGEMENT WITH OTHER CONTACT, (E) AND MAGNETIC MEANS RESPONSIVE TO CURRENT FLOW THROUGH SAID CONTACTS FOR DELAYING REENGAGEMENT OF SAID ONE CONTACT WITH THE OTHER CONTACT BY SAID SPRING MEANS UNTIL THE CURRENT THROUGH SAID CONTACTS REACHES SUBSTANTIALLY ZERO, (F) SAID SPRING MEANS URGING SAID ONE CONTACT IN A DIRECTION TOWARD SAID OTHER CONTACT IRRESPECTIVE OF THE DISTANCE THAT SAID ONE CONTACT MOVES AWAY FROM THE OTHER CONTACT WHILE SAID SWITCH-OPERATING MECHANISM IS IN ITS CLOSED POSITION, WHEREBY SAID SPRING MEANS CONSISTENTLY RETURNS SAID ONE CONTACT INTO A POSITION OF ENGAGEMENT WITH SAID OTHER CONTACT AFTER THE FLOW OF HIGH CURRENT THAT CAUSES CONTACT-POPPING. 